1. Field of the Invention
The field of the invention relates to polyamideimide polymers prepared from N,N-diacylated aliphatic, cycloaliphatic or araliphatic diamines, tricarboxylic acid anhydride compounds and aliphatic, cycloaliphatic or araliphatic diamines and to molded objects and fibers prepared from these polymers.
2. Background
Injection moldable amide-imide polymers have been prepared utilizing aromatic diamines. This is disclosed in U.S. Pat. Nos. 4,016,140 (1977) and 3,573,260 (1971). The prior art does not disclose that injection molded, melt prepared, crystalline objects can be prepared from aliphatic diamine moieties. Except for the aforecited patents, the prior art discloses that the major application of amide-imide polymers has been as wire enamels. This is illustrated in U.S. Pat. Nos. 3,817,942 (1974), 3,661,832 (1972), 3,454,890 (1970) and 3,347,878 (1967).
The general object of this invention is to provide melt prepared, ordered, linear, crystalline injection moldable polymers containing aliphatic, cycloaliphatic and araliphatic moieties. A more specific object of this invention is to provide polyamide-imide polymers containing aliphatic amine moieties which polymers are suitable for use as an engineering plastic particularly for use in injection molding and the manufacture of fibers. Another object is to provide suitable nucleating agents for the polyamide-imide polymers to enhance the crystallization rate of the ordered polyamide-imide polymers.
We have now found that injection moldable polyamide-imide polymers can be produced by reacting diacylated aliphatic, cycloaliphatic and araliphatic diamines with tricarboxylic acid anhydride compounds and aliphatic diamines, cycloaliphatic and araliphatic diamines in a molar ratio of about 1:1.95:0.9 to 0.9:1.95:1, advantageously in a molar ratio of about 0.97:2:1.03 to about 1.03:2:0.97 at a temperature of about 400.degree. to 700.degree. F. to obtain an injection moldable amide-imide polymer. The order for the addition of the reactants is not critical and all reactants can be added simultaneously or in any order desired. It has been discovered that the acylated diamine reacts preferentially with the acid groups of the tricarboxylic acid anhydride compound and that all the reactants, acylated aliphatic diamine, tricarboxylic anhydride compound and aliphatic diamine can be combined in the presence of the organic polar solvent such as dimethyl acetamide. Furthermore, acylated diamine need not be isolated or purified prior to its combination with the tricarboxylic acid anhydride compound and the aliphatic diamine.
The injection moldable linear polyamide-imide polymer of this invention comprises the following repeating structural unit ##STR1##
In the foregoing structural unit Z is a trivalent aromatic radical. Z may be a trivalent radical of benzene, naphthalene, biphenyl, diphenyl ether, diphenyl sulfide, diphenyl sulfone, ditolyl ether, and the like.
Useful aromatic tricarboxylic acid anhydrides which contribute the trivalent radical moiety of Z include those compounds containing at least one pair of carboxyl groups in the ortho position with respect to each other or otherwise situated in a fashion which permits the formation of an anhydride structure, one other carboxyl group and from 9 to 21 carbon atoms. Within these limits, these compounds may contain one or more benzenoid rings such as, for instance, trimellitic anhydride and its isomers and multi-ring compounds such as the 1,8-anhydride of 1,3,8-tricarboxylnaphthalene. Usually these compounds contain up to three benzenoid rings.
The aromatic tricarboxylic acid anhydride used in the novel process to form the polyamide-imide polymers of this invention is of the formula: ##STR2## where Z is a trivalent aromatic radical defined as set forth hereinabove. The following aromatic tricarboxylic anhydrides are preferred: trimellitic acid anhydride; 2,3,6-naphthalene tricarboxylic anhydride; 1,5,6-naphthalene tricarboxylic anhydride, and the like; 2,6-dichloronaphthalene-4,5,7-tricarboxylic anhydride, and the like. One of the preferred aromatic tricarboxylic anhydrides is trimellitic anhydride since this compound is readily available and forms polymers having excellent physical properties of tensile strength and elongation and is resistant to high temperatures.
R and R.sub.1 may be the same or be different and are divalent araliphatic, aliphatic, or cycloaliphatic radicals of from 2 to 18 carbon atoms in which carbon atoms attached to N are aliphatic carbon atoms and R.sub.2 is an aliphatic radical of from 1 to 3 carbon atoms.
R and R.sub.1 are derived from aliphatic diamines such as ethylenediamine, propylenediamine, 2,2-dimethylpropylene diamine, tetramethylene diamine, hexamethylene diamine, octamethylene diamine, nonamethylene diamine, decamethylene diamine, dodecamethylenediamine, 4,4'-diaminodicyclohexylmethane, xylylene diamine.
Low molecular weight polyamide-imides from aliphatic diamines have been prepared by a variety of methods by the prior art. However, none of these methods have produced polymers which are useful for injection molding applications. Applicants have discovered a process for the preparation of ordered linear crystalline injection moldable polytrimellitic amideimide polymers, which process comprises reacting fully acylated aliphatic, cycloaliphatic or araliphatic diamines with tricarboxylic acid anhydride compounds and aliphatic, cycloaliphatic or araliphatic diamines in a molar ratio of about 1:2:1 at a temperature of about 400.degree. to 700.degree. F., preferably 450.degree. to 650.degree. F. Optionally the polymer may be further polymerized under solid state polymerization conditions at a temperature of about 400.degree. to 550.degree. F. The resulting high molecular weight injection moldable polymer obtained has an inherent viscosity in the range of 0.4 to 3.0. For the purpose of this invention inherent viscosity is measured at 25.degree. C. and 0.5% w/v in 60/40 w/w phenol/1,1,2,2, tetrachloroethane. The term "solid state polymerization" refers to chain extension of polymer particles under conditions where the polymer particles retain their solid form and do not become a fluid mass. These polymers have excellent mechanical and thermal properties and can be readily injection molded. This injection moldability of these polymers can be partially attributed to the fact that these polymers are linear and are not cross linked. Injection molding of the polymers is accomplished by injecting the polymer into the mold maintained at a temperature of about 100.degree.-500.degree. F. In this process a 0.2-2.0 minutes cycle is used with a barrel temperature of about 400.degree. F. to 700.degree. F. The injection molding conditions are given in Table I.
TABLE I ______________________________________ Mold Temperature 100-500.degree. F. Injection Pressure 2,000-20,000 psi and held for 0.2-15.0 seconds Back Pressure 0-400 psi Cycle Time 5-120 seconds Extruder: Nozzle Temperature 400.degree. F. to 700.degree. F. Barrels: Front heated to 400.degree. F. to 700.degree. F. Screw: 10-200 revolutions/minute ______________________________________
The mechanical properties of the polymers prepared in the Examples are given in Tables 2, 3, 4 and 5.
The solid state polymerization is carried out below the melting point of the polymer and can be conducted in several ways. However, all the techniques require heating the ground or pelletized polymer below the polymer melting point, generally of about 400.degree. to 550.degree. F. while either sparging with an inert gas, such as nitrogen or air, or operating under vacuum. In applicant's process the acylated diamine need not be isolated or purified prior to its further reaction with the tricarboxylic acid anhydride compound and the aliphatic diamine. Therefore, one can react two moles of acetic anhydride or propionic anhydride and one mole of the aliphatic diamine and use the resulting diacylated diamine solution in acetic acid or propionic acid to react the two moles of tricarboxylic anhydride compound and one mole of diamine and heat the mixture to complete imidization without purification or isolation. Usually, high molecular weight crystalline polyamide-imide polymers result.
It should be noted that prior to full imidization in our process there is an intermediate polyamic acid formed of the following structure: ##STR3## and then to the injection moldable final polyamide-imide polymer disclosed hereinbefore. The values for Z and R are the same as used throughout this specification.
It has been found that to facilitate the injection moldability of the polymer produced according to applicants' novel process, nucleating agents may be employed. Without using a nucleating agent, crystalline samples can be obtained by injection molding if the mold temperature is maintained at a level of about 350.degree. to 400.degree. F. and the mold remains closed during the long crystallization part of the cycle. However, the rate of crystallization of the polymer may be so slow that the cycle time on occasion could be uneconomical. To obviate this problem, applicants have discovered effective nucleating agents. The more effective of these agents has been talc when used in about 0.01 to 10.0 weight % of the total polymer, preferably about 0.05 to 4.0 weight %. For example, it has been found that fumed silicas and zinc oxide show no effect and are useless as nucleating agents. When talc was utilized, the crystallization temperature of the polymer increased from 199.degree. C. to 223.degree. C. The use of talc as a nucleating agent lowers the induction period for the onset of crystallization of about 10 fold and also lowers the half-life from about 90 seconds to 30 seconds at 200.degree. C.